1. Field of the Invention
This invention relates to loop seams for use in joining the ends of a papermakers belt or the like.
2. Description of the Prior Art
In papermaking machines, a papermakers belt in the form of an endless belt-like structure is supported on and advanced by various machine rolls during the papermaking process. Papermakers belts carry various names depending on their intended use. By way of example, papermakers belts include forming fabrics, wet press felts, and dryer felts and fabrics. In most cases, the belt or fabric is joined at its ends to form an endless belt which is supported and controlled by various machine rolls associated with the papermaking machine.
The prior art employs various types of seams which are joined together through the use of a pintle in order to facilitate installation and removal of the papermakers belt from the papermaking machine. A very common type of seam is one employing metal clipper hooks arranged in an alternating relationship on either end of a papermakers belt to receive a pintle to join the ends of the belt together. The clipper hooks may be embedded directly into the ends of the belt, or may be secured to seam webbings which are in turn attached or secured to the ends of the belt through suitable stitching. U.S. Pat. No. 2,879,580 to Hindle is an example of metal hooks in webbing which, in turn, is stitched to the end of the belt.
Other types of arrangements for joining the ends of a papermakers belt include those in which the metal hooks are replaced by pintle receiving loops that are made from a synthetic material integral with the webbing for attachment to the ends of the belt as disclosed in U.S. Pat. No. 4,103,717 to Clark.
Yet another example is to form pintle receiving loops from the synthetic materials used to define the warp or machine direction yarns at either end of the fabric. Such seams are referred to as pin-type seams, one of which is shown in U.S. Pat. No. 4,141,388 to Romanski et al.
Still a further example is to create a seam for use in a papermaking fabric by inserting a seaming coil, removing picks in adjacent fabric areas, folding and sewing of such areas, creating a warp fringe beyond the seam area and weaving back portions of the fringe into the fabric body, Such a fabric is shown in U.S. Pat. No. 4,250,822 to Fickers.
Certain problems exist with each of the prior structures used to secure the ends of the various belts together. In some papermakers belts, the ends of the belt are joined in an abutting relationship and held that way through the use of clipper hooks inserted in a webbing, the whole of which is attached to the underside of the belt. Since the tension line of the seam is below that of the fabric, the seam tends to move upwardly so that both tension lines become coplanar. This in turn causes the abutting ends of the papermakers belt to press up against the paper sheet. When the paper sheet lies between a machine roll and the felt seam, the pressure between roll and seam increases thereby causing seam marking in the sheet, especially in the case of fine or critical grades of paper. Another problem associated with this type of seam occurs when the seam either makes or leaves the contact of a machine roll. The step caused by the sewn on webbing and the weight of the seam causes bouncing of the papermakers belt which leads to further marking of the paper sheet, paper sheet breaks, and a rapid weakening of the fabric structure in the seam area. Thread unraveling is a problem which occurs in papermakers belts in which the cut ends of the belt are exposed to either, or both, the paper sheet being formed, or the machine rolls. The last several threads in the cross machine direction at the end of a papermakers belt have the potential to become loose, a condition which may lead to further marking of the paper sheet.
Typically, in the case of a clipper seam that is attached to a papermakers belt, the sewing threads used to secure the seam to the ends of the belt are proud due to the typically hard and unyielding belt surface. Since the sewing threads are exposed on the surface of the belt and the surface of the seam, the threads are prone to wear, which ultimately leads to seam failure. The proud sewing threads can also cause paper marking problems.
In seams where loops are formed by reweaving certain of the fabric ends, certain problems exist. Certain of the fabric seams are slow to manufacture and are difficult to seam on the paper machine. In other seam types, the seam is held by sewing, which is susceptible to thread wear resulting in seam failure.
There is thus a need for a seam for joining the ends of a papermakers belt in which the chances of seam failure due to stitching failure and bounce are substantially reduced, the problem of unraveling is eliminated, and the problem of paper marking is severely curtailed. The present invention is directed toward filling that need.